The present invention relates to an antibacterial acrylonitrile fiber having the so-called photocatalytic activity where the antibacterial property is significantly improved under the condition of being irradiated with light.
As result of the recent progress in ripening and aging in the society and also in tendency of seeking the wealthy and pleasant life environment, there has been an increasing demand for maintenance and promotion of health and the appearance of clothing, bedclothes, interior products or daily commodities having clearer and more pleasant antibacterial property has been demanded.
As one of the means for giving an antibacterial property, silver ion or copper ion has been known to exhibit an excellent antibacterial property and some methods for giving an antibacterial property to fiber utilizing the characteristics of such a metal ion has been known. For example, as mentioned in the Japanese Laid-Open Patent Publications Sho-52/92000 and Hei-03/199418 as the methods for giving silver ion to an acrylonitrile fiber, there are means for providing an antibacterial acrylonitrile fiber where, in an acrylonitrile fiber having ion-exchange groups such as sulfonic acid group, carboxylic acid group and hydroxyl group, silver ion or copper ion is bonded to a part of or all of the said ion-exchange groups so that it is made remained as metal silver or copper or as a compound of the said metal.
In such a method however, although a antibacterial property is available to some extent, the product does not well meet with the recent requirement as antibacterial property and there is a problem that, in order to promote the antibacterial property, the amount of silver or copper ion to be contained in the antibacterial acrylonitrile fiber is to be increased.
An object of the present invention is to provide an antibacterial acrylonitrile fiber having the so-called photocatalytic activity where the antibacterial property can be promoted by means of light irradiation without increasing the amount of the antibacterially active metal compound.
The present inventors have carried out an intensive study for the means for improving the antibacterial property of antibacterial fiber. As a result, they have found that the above problems can be solved when an acrylonitrile fiber containing an antibacterially active metal compound is subjected to a heat treatment within a range of pH 1-6 and have accomplished the present invention. Thus, the present invention relates to an antibacterial acrylonitrile fiber having a photocatalytic activity in which an acrylonitrile fiber containing an antibacterially active metal compound is subjected to a heat treatment within a range of pH 1-6.
The object of the present invention can be also appropriately achieved by the embodiments where, in the antibacterial acrylonitrile fiber having a photocatalytic activity, the antibacterial metal compound is a silver compound, the acrylonitrile fiber has an anionic functional group and the heat treatment is wet heat or dry heat of 100-160xc2x0 C.
Best Mode for Carrying Out the Invention Now the present invention will be illustrated in detail as hereunder. With regard to the acrylonitrile fiber containing the antibacterially active metal compound used in the present invention, there is no particular limitation so far as it is a fiber which is formed from an acrylonitrile polymer and contains an antibacterially active metal compound. As to such an acrylonitrile polymer, it is preferred to use a copolymer of 60% by weight or more or, more preferably, 80% by weight or more of acrylonitrile with known monomers.
There is no particular limitation for the comonomer used for the copolymerization so far as it is copolymerizable with acrylonitrile such as other polymerizable unsaturated vinyl compounds. Thus, its examples are vinyl esters such as vinyl acetate; vinyl or vinylidene halides such as vinyl chloride, vinyl bromide and vinylidene chloride; lower alkyl esters of (meth)acrylic acid [hereinafter, xe2x80x9c(meth)acrylicxe2x80x9d means both acrylic and methacrylic] such as methyl acrylate and methyl methacrylate; acrylamide; styrene; monomers containing a sulfonic acid group such as sodium methallylsulfonate, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate and sodium vinylsulfonate; and monomers containing carboxylic acid group such as (meth)acrylic acid and maleic acid and, in order to effectively contain the antibacterially active metal compound, it is preferred that a monomer containing anionic functional group such as a monomer containing sulfonic acid group or carboxylic acid group is present in an amount of 0.1-20% by weight.
With regard to an antibacterially active metal compound, although there is no particular limitation so far as it is a metal compound having an antibacterial activity, a silver compound is preferred so that a photocatalytic activity is effectively given. Here, although there is no particular limitation for the amount of the antibacterially active metal compound to be contained in the fiber in the present invention, the amount is more preferably 1-200 m.mol/kg as a metal ion to the fiber. Thus, the content of the metal compound varies depending upon the required level of the antibacterial property and, when the amount is less than the lower limit of the range, it is difficult to achieve a noticeable photocatalytic activity in a life environment and a sufficient antibacterial property accompanied thereby while, when it is more than the upper limit, it is apt to cause a problem of a significant coloring in the heating treatment of the fiber such as drying. Further, within such a range, a sufficient antibacterial property due to the photocatalytic activity can be always achieved to daily use or industrial use and, accordingly, it results in an unnecessarily high cost and is not industrially advantageous when the metal compound is contained in more amount than the above range.
With regard to a method of making such an antibacterially active metal compound contained in an acrylonitrile fiber, there is no particular limitation and examples of such a method are a method disclosed in the Japanese Laid-Open Patent Publication Hei-03/199418 where, in the manufacture of an acrylonitrile fiber, fiber in a gel structure before drying and heat-relaxing steps is continuously treated with an aqueous solution of an antibacterially active metal salt so that the antibacterially active metal salt is made contained in the fiber and a method disclosed in the Japanese Laid-Open Patent Publications Sho-52/92000 and Hei-07/243169 where an acrylonitrile fiber is manufactured by a conventional method and then subjected to an after-treatment so that an antibacterially active metal compound is made contained therein.
In the present invention, it is necessary that the acrylonitrile fiber containing the antibacterially active metal compound manufactured as such is subjected to a heat treatment at a range of pH 1-6 or, preferably, pH 2-4. Although there is no particular limitation for the said heat treatment, a method of treating with wet heat or dry heat of 100-160xc2x0 C. is preferred and its examples are a method where an acrylonitrile fiber containing the antibacterially active metal compound is impregnated in an acidic aqueous solution of pH 1-6, water is drained off therefrom and the fiber is subjected to a wet heat treatment by steam in an autoclave and a method where the fiber wherefrom water is drained off is immediately subjected to a dry heat treatment using a hot air drier. The treating time is set depending upon the treating temperature.
When the pH at this heat treatment stage is less than 1, physical property of the fiber is significantly deteriorated while, when it is more than 6, the photocatalytic activity is not given whereby the present invention is not achieved. When the heat treating temperature is lower than 100xc2x0 C., the treating time becomes long and that is not an industrially advantageous method while, when it is higher than 160xc2x0 C., physical property of the acrylonitrile fiber is deteriorated.